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Bunuel
In each of 3 bags, there are 2 green disks, 3 blue disks, and nothing else. If one disk is chosen at random from each of the bags, what is the probability that not all of the disks chosen are green?


A. \(\frac{8}{125}\)

B. \(\frac{36}{125}\)

C. \(\frac{108}{125}\)

D. \(\frac{117}{125}\)

E. \(\frac{124}{125}\)

all are green ; 8/125
and not green 1-8/125 ; 117/125
IMO D
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Solution

Given:
    • Total number of bags = 3
    • Each bag has
      o 2 green disks
      o 3 blue disks

To Find:
    • The probability that not all of the disks chosen are green, if one disk is chosen at random from each of the bags

Approach & Working Out:
    • The probability that not all of the disks chosen are green = 1 – the probability that all the three disks chosen are green = \(1 – (\frac{2}{5}) * (\frac{2}{5}) * (\frac{2}{5}) = 1 – \frac{8}{125} = \frac{117}{125}\)

Hence, the correct answer is Option D
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Bunuel
In each of 3 bags, there are 2 green disks, 3 blue disks, and nothing else. If one disk is chosen at random from each of the bags, what is the probability that not all of the disks chosen are green?


A. \(\frac{8}{125}\)

B. \(\frac{36}{125}\)

C. \(\frac{108}{125}\)

D. \(\frac{117}{125}\)

E. \(\frac{124}{125}\)

We can use the formula:

P(not all of the disks chosen are green) = 1 - P(all of the disks chosen are green)

Since P(all of the disks chosen are green) = 2/5 x 2/5 x 2/5 = 8/125, then P(not all of the disks chosen are green) = 1 - 8/125 = 117/125.

Answer: D
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Bunuel
In each of 3 bags, there are 2 green disks, 3 blue disks, and nothing else. If one disk is chosen at random from each of the bags, what is the probability that not all of the disks chosen are green?


A. \(\frac{8}{125}\)

B. \(\frac{36}{125}\)

C. \(\frac{108}{125}\)

D. \(\frac{117}{125}\)

E. \(\frac{124}{125}\)
P(G)=2/5 from each bag
P(G) from all bags=8/125
P(Not all G)=1-8/125=117/125
=117/125
Or we can use the time consuming method:)
Blue, Blue, Blue- 27/125
Blue, Blue, Green- 3/5*3/5*2/5*(!3/!2)-54/125
Blue, Green, Green-3/5*2/5*2/5*(!3/!2)-36/125
Total=27+54+36/125
=117/125
D:)
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